It has been the practice in the art to cast a plastisol film or foam suitable for use as a tape product, such as a bandage or wound dressing, on a casting sheet in a first stage on one apparatus, and then deliver the laminate to a second apparatus in roll form. The casting sheet is conventionally a siliconized paper about 60 inches wide, and several thousand yards long, impregnated with clay or some other saturant, to provide a smooth surface for the cast.
On the second apparatus, the roll of the film or foam/casting sheet laminate is mounted for contacting with a liner (such as a kraft paper on the order of about 60 pounds), which liner is first coated on one side with a release layer, such as a silicone compound, and then coated with an adhesive on top of the silicone. The film or foam is then laminated in the second stage to the adhesive layer, such that the film or foam is interposed between its casting sheet, or carrier, on one side, and the adhesive layer of the new adhesive coated liner on the other side. The casting sheet, or carrier, is then stripped off of the laminate, and is discarded.
If the tape product is to be used as a bandage or wound dressing, the rolled sheet is perforated (such as being rolled with pins) and then is cut to size, in one application on the order of 31/4 inches wide, although the width could vary. The length of the bandage, is thereafter cut from the width of the roll, in a third stage. The narrow laminate is conventionally wound in large rolls, for delivery to a third apparatus.
In a third stage, the heavy liner is stripped off the narrow laminate. The adhesive sticks to the film or foam, but not the liner. In the case of a bandage, an adsorbant pad is applied to the adhesive, and a new about 40 to about 50 pound liner, comprising two overlapping pieces that form the "pull tab", is laminated. The new laminate is then passed to a cutter, or a die.
In one embodiment, the plastisol foam comprises foamed polyvinyl chloride, or PVC foam. PVC foam is conventionally cast at the relatively high temperature of about 300.degree. to about 400.degree. F., requiring a dense casting surface with easy release. Otherwise, the resulting PVC foam will not form a flat, glossy sheet as desired, as water vapor or bubbles adsorbed on the casting sheet will be taken up in the foam. Also, if a dense casting sheet is not utilized, an easy release will not be effected in the stripping process in the third stage.
In the conventional process, a rate limiting step is stripping off the heavy casting sheet during the second stage, at the point that the film or foam is laminated to the adhesive coated release liner. Further, the heavy, treated casting sheet is normally discarded. It is therefore desirable to bypass the rate limiting procedure. It is further desirable to economize by avoiding the use of the heavy, extra casting sheet, such that the cost of both its purchase in the first instance, and its disposal after use, are avoided.
A further disadvantage to the conventional process is that it is necessary, during the second stage, to splice both the liner and the film or foam, when each reaches the end of the rolls on the apparatus. The spliced section passes through to the third stage and into the finished product. These spliced products must be culled out of the product before packaging and/or delivery to the customer. This culling process causes additional wastage and the slowing of run speeds, resulting in inefficiencies in the process.
Another disadvantage in the conventional process, that is, utilizing a preformed film or foam on a casting sheet, is the requirement that the adhesion of the film or foam to the adhesive coated release liner be more tenacious than the adhesion to the casting sheet, so that the casting sheet can be stripped off without delaminating the film or foam from the liner. This balance is difficult to achieve. Also, too high an adhesion to the liner will make conversion of the tape laminate to, for example, a bandage type product more difficult, as the release liner must then be stripped from the tape.
Tape products currently used in the industry which are affixed to electrodes for the purposes of medical diagnosis or drug delivery have several distinct limitations. Changes to the tape product construction, such as swelling or shrinkage of the various component layers, often results in the modification of the electrode signal and exposing the patient to a risk of electrical shock from the electrode. Furthermore, many tape products for electrodes experience a loss of adhesive integrity due to the changes in the component layers. Therefore, it is desirable to develop a tape construction useful for fabrication of medical electrodes to be adhered to human skin, which overcome the limitations and disadvantages of the tape products of the prior art.